Signaling system



Nov. 29, 1938.

H. M. PRUDEN S IGNALING SYSTEM Filed May 14, 1957 lA/VEN 70/? H. M. PRUDE N ATTORNEY Patented Nov. 29, 1938 UNITED STATES PATENT OFFICE SIGNALING SYSTEM Application May 14, 1937, Serial No. 142,619

This invention relates to signaling systems and particularly to signal receivers adapted to respond to signaling currents of a particular frequency.

It is the object of the invention to provide a more reliable signal receiver adaptedto respond to signaling currents of each of a plurality of frequencies without responding to nonsignaling currents of the same or other fre-v quencies.

It is, of course, known to use alternating'current for signaling over telephone lines and moreover to signal with current within the voice frequency range. It is necessary in such signaling arrangements to provide means for preventing false operation of the signal device in response to voice currents which include the particular voice frequency which is being used for signaling. When two or more'different types of signals are required, a different frequency may be used for each type of signal.

This invention is a multi-channel signal receiving circuit arrangement comprising two signal receivers, amplifier-coupled to an incoming line, each of the signal receivers comprising a thermionic tube andan impedance bridge connecting the tube to the output of the amplifier. The bridge of each receiver is balanced to current of a different particular frequency and unbalanced to currents of all other frequencies and is directly connected to the grid of the tube in such a manner that the signal device is operated only when the current in the signaling circuit is of the particular frequency and does not include other frequencies. A feature of the invention is the provision of rectifying elements in the thermionic amplifier for controlling the potential applied 'to the grid element of the thermionic tube of each of the signal devices.

Further explanation of the invention will be made by considering a circuit arrangement in which the invention is embodied, such an arrangement being shown schematically in the drawing which forms a part of this specification.

The invention is, of course, not limited to the specific arrangement shown in the drawing and is, in general, applicable to all signaling sys- 'tems comprisinga signal receiver responsive to signaling current of a particular frequency.

The drawing which consists of a single figure shows a multi-channel signal receiver which comprises an amplified A and two differently tuned signal receivers Cl and C2.

The incoming signaling circuit includes the line L and the primary windings of an input transformer 9'. The thermionic tube III of amplifier A comprises a filament, a grid II, a grid-. controlled anode, or plate, |2 and two rectifier plates I3 and M. The secondary windings of the input transformer 9 are connected in thegridfilament circuit of tube III which circuit also. includes the grid biasing battery I8. The circuit for heating the filament of tube I0 is not shown but includes any suitable source of current. The output of the amplifier is divided by means of a 10 hybrid coil group comprising transformers 20 and 40 and the balancing resistor 60. The balancing resistor 60 has a high resistance and is connected in series with the balancing winding 24 of transformer 20 and the balancing winding 44 of transformer 40. The anode-filament circuit of tube Hi includes the primary winding 2| of transformer of signal receiver Cl and the primary winding 4| of transformer 40 of signal receiver C2 and the battery IS. The volt- 20 age ratio of the .input transformer 9' and the grid biasing potential are so related that signaling current received at the highest normal level will not cause overloading of tube Ill.

The signal receiver C], which comprises a 25 thermionic detector andsignal relay 3|, is operatively responsive to signaling current of one particular frequency, such as 1200 cycles; and the signal receiver G2, which comprises a thermionic detector 50 and signal relay 5|, is opera- 30 tively responsive to signaling current of another particular frequency, such as 1800 cycles. The grid of tube- 30 is inductively coupled through secondary windings 22 and 23 oftransformer 2|],

and the grid of tube 50 is inductively coupled through secondary windings t2 and d3 of transformer 10, to the output circuit of amplifier tube ID. The battery 63 furnishes the normal grid bias for tubes 30 and 50. The circuit or circuits for heating the filaments oftubes 30 and 50 are not shown but include any suitable source of current. The output, anode-filament circuit or tube 30 includes the winding of signal relay 3| and plate battery 64; and the output, anodefilament circuit of tube 50 includes the winding .of signal relay 5| and battery 64.

The secondary windings 22 and 23 of trans- I I former 20 constitute adjacent branches of an increases the negative potential ofthe grid of tube 30. The resistor 29 has a high resistance and serves as a grid leak resistance. The windrent of 1200 cycles.

ings 22 and 23 are alike and have the same im-' pedance' at all frequencies; the'resistor 25 is noninductive and. has a high and constant impedance at all frequei cies; and the condenser 26 and coil 21 are tuned to ofler a high impedance to cur- Therefore, the impedance of network 2G2'i, t'o signaling current of 1200 cyclesis substantially equal to the impedance of resistor 25, so that little or no difference in potential exists between points a andb of the bridge when signaling current of 1200 cycles and no other frequency is being received. But the bridge is unbalanced to current of all other frequencies and a drop in potential exists between points a and b when current of afrequency other than 1200 cycles is being received'because the impedance of network 26-27 decreases rapidly with only a small change in the frequency above or below 1200 cycles. The drop in potential across network 26- -27 is impressed on the grid of tube and, when signaling current of 1200 cycles andno other is being received over line L, the filament-anode current causes the'operation ofsignai relay iii. of a frequency other than 1200 cycles-is being received the difierence in potential between points a and b is effective during one half of each cycle to charge condenser 28 in a direction to increase the negative bias on the grid of tube 30 and thereby prevent the operation of signal relay iii.

The secondary windings 32 and d3 of transformer 30, the resistor 55 and the network comprising condenser 46 and induction ,coil 6? also constitute an impedance bridge. The condenser and coil 67 are tuned to offer a high impedance to current of 1800 cycles. The resistor 45 is noninductive and has a high and constant impedance, so that the bridge is balanced to current of i 1800 cycles and unbalanced at all other frequencies. The rectifier plate i land filament of amp er tube ID are connected inseries with con enser 48 and grid leak resistor 49 across No potential difpoints 0 and d of the bridge. ference is created across points 0 and d by current of 1800 cycles and signaling current of this frequency and no other causes operation of signal relay 5!; but current of otherfrequencies causes the charging of condenser 48 in a direction which increases the negative bias of tube 50' and the operation of signal relay Si is thereby prevented if the current received over line L consistsof or includes frequencies. other than 1800 cycles.

When, therefore, a 1200 cycle signaling current is received over. line L and there are no other frequencies being received, the detector tube 30 causes the operation ofsignal relay 3| but tube 50 is ineffective to operate signal relay 5!. When an 1800 cycle signaling current is received over line L and there are no other frequencies being received, thedetector tube 50 causes the operation of signal relay 5| but tube 30 is ineffective to.operate relay 3!. Andwhen current of both of, these frequencies, or of either of these frequencies and also current of other frequencies, is. being received 'over line L, both of the tubes 30 and 50 are ineffective to cause the operation of signal relays 3i and 5|.

Such an arrangement is adapted for use in But when signaling current.

amacie and filamentof amplifier tube ill in series with selectively responding to dial impulse signals and to supervisory signals, transmitted over toll lines, only one of these types of sifiials being transmitted at a time. 4 I

What is claimed is? 1. In combination, a signaling circuit, a thermionic amplifier for amplifying signals incoming the same potential when the bridge is subjected to current of said signaling frequency and at different potentials when the bridge is subjected to current of other frequencies for preventing the operation of said relay when the incoming signaling-currentincludes frequencies other than said signaling frequency...

i2. In combination, a signaling circuit, a thermionic amplifier for amplifying signals incoming over said circuit, two signaling relays, a first thermionic device for operating one of said relays in response to signaling current of a first particular frequency, a second thermionic device for operating the other of said relays in response to signaling current of a second particular frequency, means comprising a' first impedance bridge balanced at said'first frequency and unbalanced at other frequencies for coupling the output of said amplifier to said first device, means comprising a second impedance bridge balanced at said second frequency and unbalanced at other frequencies for coupling the output of said amplifier to said second device, means comprising a capacitor and a rectifier connected across points of said first bridge which are at the same potential if the incoming signalingcurrent is of said first frequency-and at different potentials if this current includes any other frequency for preventing.

the operation of said first relay when the incom-v ing signaling current includes frequencies other than said first frequency, and means comprising a capacitor and a rectifier connected across points of said second bridge which are at the same potential if the incoming signaling current is of said second frequency and at difierent potentials if this current includes other frequencies for preventing the operation of said second relay when the incoming signaling current includes frequen-.

cies other than said second frequency.

3. In combination, a line, a transformer, a thermionic amplifier, a signaling circuit including said line and a primary winding of said trans formerya secondary windingof said transformer connected to the grid of said thermionic ampli fier, a second transformer, the plate? circuit of said thermionic amplifier including a primary winding of said secondtransformer, an impedance bridge, two like secondary windings of said second transformer constituting adjacent branches of said bridge, a non-inductive resistor of low conductivity constituting a 'third branch of the bridge, a tuned network comprising a condenser and an induction coil connected in'parallel constituting the fourth. branch of said bridge, said tuned network having-maximum impedance at a particular signaling frequency, a rectifier plate in said thermionic amplifier, a detector tube, a

grid condenser and grid leak resistor for said detector tube, said grid condenser and grid leak resistor in parallel being connected in series with the filament and rectifier plate of said thermionic amplifier across the junction point between the secondary windings of said secondary transformer and the junction point between said non-inductive resistor and said network, the grid of said detector tube being connected to the junction point between the secondary windings of said other transformerand said network, and a signal relay connected in the plate circuit of said detector tube for operation when the current in said signaling circuit is of said particular frequency and no other.

4. In a combination according to claim 3, a third transformer, a primary winding of said third transformer being included in the plate circuit of said thermionic amplifier, two like secondary windings of said third transformer constituting adjacent branches of a second impedance bridge, a second non-inductive resistor of low conductivity constituting a third branch of said second bridge, a tuned network com-' prising a condenser and an induction coil connected in parallel constituting the fourth branch of said second bridge, said second network having maximum impedance at a second particular signaling frequency, a second rectifier plate in said thermionic amplifier, a second detector tube,

a grid condenser and grid leak resistor for said second detector tube, the grid condenser and thegrid leak resistor of said second detector tube being connected in parallel with each other, and in series with the filament and second rectifier plate of the thermionic amplifier across the Junction point between the secondary windingsf of said third transformer and the junction point between said second non-inductive resistor and said second network, the grid of said second detector tube being connected to the junction point between the secondary windings of said third transformer and I said second network, and a second signal relay, said relay being operatively controlled by said second detector tube.

5. In a signaling system, a signaling circuit, a thermionic amplifier, the grid of said amplifier being connected to said circuit, a plurality of signal receivers, one for each of a plurality of signaling frequencies transmitted in said circuit, a transformer for eaclr of said receivers, a primary winding of each of said transformers being included in the platecircuit of said thermionic amplifier, a rectifier plate in said thermionic amplifier for each of said signal receivers, each of said receivers comprising a signal relay,'a detector tube, a condenser, and an impedance bridge balanced at the particular signaling frequency to which it is desired that said relay be operatively responsive and unbalanced at all other frequencies, said condenser being connected in series with the associatedrectifier plate and the filament of said thermionic amplifier across points of said bridge which are at equal potential when the current in said circuit is of said particular signaling frequency and at difierent potentials when the current is of any other frequency in such a manner as to prevent energization of the signal relay when the current 'in said circuit includes frequencies other than said particular frequency.

HAROLD M. PRUDEN. 

